The efficiency of five isolates of Bacillus spp. isolated from the most important agricultural pests in Alexandria and Beheira re­gions,Egypt were evaluaed, for the first time to conrol the 4th larval in-star of the cotton leafworm, Spodopter littoralis Boisd. under laboratory conditions. The results indicated that Bacillus thuringiensis var. Kurstaki (H3a, 3b) was more effective on the larvae of S.littoralis than the other species.At the highest concentration (12 x 10⁷ spores/m1), percentages of mortality reached 90, 86.66, 76.66, 70 and 53.33 with B, thuringiensis var. Kurstaki, B.sphaericus, B.pumilus, B.megaterium andB.coagulans, respectively after 7 days from treatment. Whereas, the L.C50 value for B. thuringiensis var. Kurstaki (1.10 x 10⁷ v_s./m1) was less than that of B.coagulans (9.00 x 10⁷ v.s./ml). So, this bacterium B.thuringlensis var. Kurstaki was more effective on the death of the 4th larval instar of Slittoralis. Therefore, the pathogenicity of these bacterial strains can be used as microbial control agent against .5.11U^-crab's.